Overwintering Pieris Plants

Winter Hardiness

• Pieris shrubs need a cool winter dormancy period in order to grow full of health and vigor and produce flowers by spring. They are grown outdoors in U.S. Department of Agriculture plant hardiness zones 4 through 8. Pieris japonica is less cold hardy, surviving in zones 5b through 8b, while Pieris andromeda grows best in zones 4b through 8a, where temperatures are slightly cooler in all seasons. Excessive cold kills back branches, dries out leaves and will even kill roots. Once roots die, no rejuvenation can occur in the spring.

Healthy Overwintering

• Healthy, disease-free and unstressed pieris shrubs survive winter the best and with the least complications. Growing the shrubs in an evenly moist, fertile soil during the year establishes the best root systems as well as the healthiest leaves and twigs. A slow transition from summer's warmth to winter's subfreezing temperatures across a gradually cooling fall is best. Do not allow shrubs to enter winter stressed by overly dry soil. Once soil freezes, you cannot water and tissue desiccation increases. Dry, cold winds in winter also quickly leads to leaf and twig desiccation.

Container Issues

• Pieris plants grown in containers at the nursery or displayed in attractive pots in the garden are more susceptible to winter cold and desiccation compared to plants in the ground. As long as the soil is not frozen, continue to irrigate container-grown pieris to keep its roots evenly moist. Move plants out of drying winds and afternoon sunlight in winter. The limited soil volume in a container provides less insulation from cold air temperatures. Once the soil freezes and drops to a temperature of 10 to 15 degrees Fahrenheit, expect at least 50 percent of the root system to die.

Overwintering Tips

• To increase overwintering of pieris shrubs in the ground, site them properly at planting so they are not in a wind-exposed, cold microclimate during the winter months. A snow fence or burlap screen near the shrubs can diminish the drying effects of winds. Snow insulates plants from cold. Containerized shrubs need to be relocated to milder locations to prevent excessive drying and freezing of the root ball over the winter. Heeling pots into the soil for added insulation or mounding dry mulch over the containers shields plants from cold too. Always irrigate the soil when the soil is not frozen to ensure the dormant roots do not die from desiccation.